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From biyuhao (GitHub) <git...@apache.org>
Subject [GitHub] [incubator-dubbo] biyuhao commented on issue #2938: Improve several map iteration
Date Tue, 11 Dec 2018 10:49:49 GMT
@beiwei30 
I think this makes us a more unified code style and gain a better performance.
I did a little google search and got some betters answers than mine.

1. ["entrySet()" should be iterated when both the key and value are needed
](https://rules.sonarsource.com/java/tag/performance/RSPEC-2864)
> When only the keys from a map are needed in a loop, iterating the keySet makes sense.
But when both the key and the value are needed, it's more efficient to iterate the entrySet,
which will give access to both the key and value, instead.

2. [Performance Comparison of Different Ways to Iterate over HashMap](https://howtodoinjava.com/java/collections/hashmap/performance-comparison-of-different-ways-to-iterate-over-hashmap/)
>Using entrySet() in for-each loop : 50
Using keySet() in for-each loop : 76
Using entrySet() and iterator : 50
Using keySet() and iterator : 75

3. [performance-considerations-for-keyset-and-entryset-of-map](https://stackoverflow.com/questions/3870064/performance-considerations-for-keyset-and-entryset-of-map)
>Here you first need to get hold of the set of keys. This takes time proportional to the
capacity of the map (as opposed to size for the LinkedHashMap). After this is done, you call
get() once for each key. Sure, in the average case, with a good hashCode-implementation this
takes constant time. However, it will inevitably require lots of .hashCode and .equals calls,
which will obviously take more time than just doing a entry.value() call.

At last, I have not done such a profiling. So I think it's more about unifying code style
here.
This is a trivial change, it's on your call. 😃 

[ Full content available at: https://github.com/apache/incubator-dubbo/pull/2938 ]
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